3 phase workshop wiring

[wallace]

Hi all and a happy new year to you all. I have grand plans to rewire my workshop for my 3 phase machines. At the moment everything is wired in a daisy chain fasion. I plan on having a distribution board with mcb for each machine. I am going to run trunking around the shop to house the 3 phase and single for the sockets. What size wire should I be using for the 3 phase. Most machines will be within 5 metres of the dist board but the planer which creates the biggest load on starting will be 13m away. I think the biggest motor is on the spindle moulder at 5.5hp.
thanks

 

[HappyHacker]

Happy New Year.

I would recommend getting a local electrician in to make recommendations and do some or all of the work. There are a number of questions that need answers apart from the cable size: grouping factors, RCD requirements, how is the equipment to be connected and isolated, earthing and bonding requirements which depend on the type of earth provided by the supplier.

In addition if the workshop can be considered domestic then Part P of the building regulations will apply but no ever bothers to police it. Getting a Part P registered "electrician" unfortunately does not mean they will know anything about three phase.

If you find the right electrician they may be happy for you to do a lot of the work while they connect it up, test it and provide you with the appropriate Electrical Installation Certificate (EIC) as well as doing the Part P registration.

Kevin

 

[RobinBHM]

When I rewired my joinery workshop I ran 75mm x 75mm trunking down both sides. Each machine drop was done with round plastic conduit 25mm, which is quite easy, just drill a 25mm hole in the trunking and run the conduit straight down to the machine isolator. Every machine is on its own radial circuit and therefore has its own mcb (some C rated I think).

Running in trunking and conduit means all the wiring can be run in singles which makes it simple. I think most of the cables I used were 4mm, but the runs were quite long and some of the machines have big motors. You might find 2.5mm may be okay, but you will need to do the sums. As Kevin mentions, there are a number of factors including grouping etc but the basic requirement is that the mcb should always be lower than the cable rating and the mcb size is obviously decided by the machine requirement. If you are buying 100m rolls of cable it may just work out cheaper to run each radial in 4mm if thats enough for the larger machines.

 

[mikefab]

Wallace, I'm not so far away from you (Hexham), and recently used a local electrician to wire a couple of 3 phase machines in from my 3 phase converter via a three phase distribution board. He used to work as an industrial electrician and has an elec engineering degree so knows what he is on about. He made a nice job of putting isolators and kick-stop switches onto the machines too. I'd be happy to share contact details with you if this would help.

Mike

Sent from my SM-G920F using Tapatalk

 

[wallace]

Thanks chaps, Mike thanks for the offer but I like to do the stuff myself. I will probably get it looked over. I bought a load of isolators a while back. I think the pricey bit will be the cable. It soon adds up with 4 wires per machine and 13 machines, that's 52 lengths going from 5 to 15 metres. :shock:

 

[wills-mill]

I've done a fair old setup from a 15hp rpc last year. We decided to go with everything on 415v red sockets, with all sockets and cabling (SWA armoured) set up to take 32 amps, just in case anything beastly needs to be moved around or plumbed in. The overkill makes a fairly minimal difference compared to the thought of having to change and faff around at a later date. The sockets are an expense compared to hard wiring machines, but they are very forgiving, as it's dead easy to change machine leads or leave plenty of spare on the flexible lead (using SYA cable, which is great stuff).

We used these Gewiss units, happy with them but when a plug is in it stands out into the room quite a bit, and could be vulnerable to damage. http://www.ebay.co.uk/itm/Gewiss-32A-41 ... SwQItT4LDr

Bear in mind that every circuit/ machine needs to have an isolator at hand near the machine.

The setup looks a little odd, as there's a diddly 240v consumer unit that feeds the converter which in turn feeds up to a serious 3 phase board. My sparks was very happy for me to source second hand board and MCBs, I got my fingers mildly burnt by buying an older board (made by BILL) that wasn't compatible with more recent BILL/ MEM/ Eaton MCBs. The three phase MCBs can end up being a massive cost if bought new and are quite spendy second hand. It's best to pay close attention to the model numbers of the MCB units and try and pick them up as they come up for sale, I've got 4 unused MEM 32A EMCH332 type C breakers available if you head that way.

If you've not been near them before the type (A,B,C, or D) is important, as it's a measure of how tolerant the breaker is to starting overload/ current spikes before it'll trip. If you try and wind up a large planer on a cold day, then you need to be on type C, A and B's are tolerant of domestic loads, C for heavy motors and D for things with brutal initial laods like large welders.

Most of the cable runs on my setup are on cable tray fixed flat to the wall, with a few spacing washers behind so that cable ties can be passed through. Our local electrical factor was far and away the simplest and cheapest supplier, most of the ebay 'deals' were hamstrung by delivery costs and very expensive.

 

[wills-mill]

If you do head towards sockets in any way, it's worth fitting 5 pin sockets and plugs from the start, just in case you ever meet a machine that would like 3 phases, neutral and earth. It's unlikely with Uncle Wadkin, but it's nice to have that pin, even if it doesn't have a wire run to it.

 

[wallace]

Thanks William, I have the single 4pin sockets at the moment http://www.ebay.co.uk/itm/2x-16A-AMP-4- ... cZWeQ7Zbut they feel a bit cheap and nasty and I don't like them. I've got some nice old cast MEM isolators much more in keeping with my old wadkin lumps. I did get a dist board, I think I got a good mix of MCB's

 

[n0legs]

If you're looking for plugs, IMO the MK Commando is about the best available, Around £8-9 from TLC for the 32a.
The Doncaster cables site has a useful calculator for cable sizes. Bear in mind the current ratings will be running current and not start up current, so some allowance will need to be factored in. http://www.doncastercables.com/technical-help/.

If it's just you in the workshop and you will be unlikely to run more than one machine at a time, I wouldn't get too hung up on grouping factors. If you use sensible size cable you'll find it very difficult to heat them up.

Marshall Tufflex 50 x 50 plastic trunking should be ample, it's a nice neat size for use around the top of a room or even around the middle. Also very easy to join conduit to it. Metal trunking is nice but install is more involved and if you're not a full commercial/industrial set up why bother.

C type breakers will be your friend and make sure they're lower rated than the cable used for each circuit.

Masking tape, get some. Use it to identify the circuits inside the trunking. I've seen so many installs that look like a pigs guts. Circuit name and current rating every metre or so wrapped around the group of cables helps a lot.